Sign language is an expression of series of signals (facial expressions, body movements or body Language, hand shapes, hand positions, hand movements and gestures) to communicate an idea to any other person who is not otherwise able to interprets the idea and to act sensibly on it. Each gesture shows something specific, an object or an action and grouped together, a sentence. To be able to see therefore is critical to the interpretation of the message as is the case where hearing is critical to interprets speech. In both cases one needs to be acquainted in the specific language offered.
With gesture we could attempt to convey a certain need to a person who is not acquainted to any language we may speak e.g. in a foreign country. There seems to be no disability but only for the fact that we do not speak each others languages.

In the same way, someone might have perfect hearing abilities but a brain dysfunction to interprets vocal auditory sounds and thus could not understand when we converse our message. Mainly, sign language has been developing in the same way as spoken language over a long period of time, to help Deaf people and people with hearing disorders and in a specific culture.

Sign language consists of vocabulary, grammar and pronunciation the same way as any existing, living language but for the difference, pronunciation are in expressions and gestures.